Aperture is referred to the lens
diaphragm opening inside a photographic lens. The size of the diaphragm opening in
a camera lens REGULATES amount of light passes through onto the film inside the camera
the moment when the shutter curtain in camera opens during an exposure process. The
size of an aperture in a lens can either be a fixed or the most popular form in an
adjustable type (like an SLR camera). Aperture size is usually calibrated in f-numbers
or f-stops. i.e. those little numbers engraved on the lens barrel like f22
(f/22),16 (f/16), f/11, f/8.0, f/5.6, f/4.0, f/2.8, f/2.0, f/1.8 etc. Each of this
value represents one time the amount of light either more or less in quantity. Meaning
to say, f/16 will let in 1X the amount of light than a diaphragm opening of
f/22 and so forth; while on the other hand, an aperture of f/4.0 will let in 1X lesser
than that of f/2.8 etc.

Note: the diaphragm blades inside this manual
focus Canon FD lens control the amount of light passing through the lens that eventually
hitting to the film during an exposure process. The 'amount', or simply explained
in layman term - opening changes according to selection of aperture (f/number).
In this case, it is indicated by the f-numbers that imprinted on the lens barrel.

LENS SIDE:- If
a simple word "diaphram" can be confusing to you, just try to think numbers
engraved on the lens barrel are NOT referred to aperture diaphragm
BUT rather, there are just number to let you refer the size of the lens diaphragm.
So, if you are new to this, just memorize these numeric settings that will do, as
they represent the corresponding size of the lens diaphram inside the lens and let
you determine and control how much light you would require to let into the camera
for a proper exposure by way of selecting an appropriate aperture diaphragm from
large to small (lens opening). But
technically, these numbers refer to the relative physical opening of the lens diaphragm.
So, don't worry about the confusing part of them.

NOTE:- When you are one level up:-
*.. These numbers are very significant
to the lenses because they are calculated based on the properties of the lens they're
on. f/5.6 on a wide angle lens will not have the same diameter as another, say on
a long lens. There are simple lens formulas which help calculate the different properties.
But the f number diameter is unique to each lens..". Benoit Aubry (benoit_aubry@hotmail.com
but I would rather teach a new budding photographer whio may be interested in picking
some pieces rather than serving technical request of a more seasoned photographer.
But ant=yway, thanks, pal.

Modern Autofocus
SLR cameras may have a different ways in manipulating the aperture. One of the trend
is - the aperture value is now control via a thumb wheel on the camera (usually near
the shutter release button) and the AF lens has no aperture ring to alter the value.
Each camera manufacturer usually has their own series of lenses under a trade name
to verify its usage, various compatibility issues with their previous camera model's
function etc. For an instance, Canon manual focus lenses are called
"FD" or "FL";
while their newer series of autofocus lenses (AF) designed for their Canon
EOS Series
cameras are referred as "EF" (Electro Focus). Each of these MF/AF
lenses has their own respective way to illustrate the control of aperture in the
camera. When you turn the aperture ring on a lens to vary the aperture, you will
be able to check visually the set opening of the lens diaphragm (Opens bigger or
stopping smaller).
*here in
this section, I am confining the discussion
within the MANUAL FOCUS lenses ONLY
because the proportion of used equipment forms the basis for a cheap, easy entry
for potential new serious photographers.

* Some lenses such
as those made by Canon (See above), the lens diaphragm will not react to turning,
unless you press the aperture pin.

There are many camera
brands out in the market, thus, it is indeed very difficult for me to compile all
of the labels into a single site. Anyway, I am using three popular camera brands
to illustrate the whereabouts of these aperture on the lens. (A)
is a typical FA
lens by Pentax;
(B) is a typical manual
focus Nikkor zoom lens
from Nikon; while the (C) is a Zuiko lens by Olympus.

Reminder:-
the key to an theoretical good EXPOSURE = Aperture + Shutter speed

Remember: For a theoretical "perfect"
exposure to be formed i.e. nice
colour balance, every details shown or simply a photo that you are happy about, take
a good combination between using an aperture with the appropriate matching shutter
speed for any given film speed (ASA/ISO) are required. The latter refers to the film
speed of the film roll used. i.e. ASA 100, ASA 200, ASA 400 etc. the faster the film
speed used, you can use to capture lower lighting situation but at the expense of
grainer output of prints / slides. Next, a little confusion may create for you
to learn here: - each step increment in the use of film speed will also indirectly
correspond with one step of aperture OR shutter speed.

I know you must be
asking a mind boggling question while you read until here: Ooi....HOW THE HELL WOULD
I KNOW WHAT
APERTURE TO SET
on my lens when I take a picture ? Frankly, you need not have to ! Inside
any modern camera, there is a metering cell residing internally which measures the
light intensity of the scene you are trying to capture/pointing to. Its metering
circuitry will SUGGEST an exposure for you. For an instance, the exposure suggests
by the camera's internal metering circuitry indicates 1/125 sec. (camera) with f/8.0
(lens) will deliver a decent exposure for your intended capture. You can override
the camera setting (depends on whether the camera has such option for you to manipulate
the aperture on the lens OR shutter speed on the camera, most P&S don't offer
such options but a SLR camera usually does). For an example, change the f/8.0 to
f/4.0 (let in more light by 2 steps 4.0-->5.6-->8.0) and compensate the shutter
speed by few stops by limiting light entering the camera shutter i.e. 1/125--->1/250--->1/500.
The compensated 2 steps on the shutter speed still delivers the SAME EXPOSURE
as the earlier camera suggested reading. The difference is now with a f/4.0, you
can achieve a narrow Depth of Field (refer to below WHY and WHAT difference it will
bring to your picture with such alternation)..

However, the MOST confusing part for any new photographer
is: Just remember in photographic term: a
BIG aperture is actually referring to a smaller number engraved on the aperture ring
of the lensi.e. f/1.4,
f/2, f/2.8, f/4.0 etc. while small
apertures mean bigger numbers
i.e. f/22, f/16, f/11, f/8 etc. Once you have "overcome" such "mental
block" in calculation, it should help you greatly understand / enjoy reading
more in other sections that follow. So, it is important that you OUGHT to digest
this paragraph.
(CLICK HERE to understand the relation
of those numbers found on the lens where how the lens diaphragm inside at each aperture
set. Well, I am not sure who was the hell was the bloody smart guy who first
started by inverting the number on the aperture on the lens - where small number
(f/2.0, f/2.8 etc.) is actually referring to a larger lens opening while big number(s)
such as f/11, f/16, f/22 etc. is actually smaller aperture. Basically, large aperture
(f/2.0, f/2.8 etc.) lets in more light to the camera shutter for an exposure, while
small aperture (f/11, f/16, f/22 etc.) has a smaller opening in the lens diaphragm
to let in LESS light for a given exposure. The confusion usually causes a beginner
who might be poor in mathematics gives up serious photography from here @#$^*#&*!!.
Well, I guess you are not within that figures-fophia group, so - why don't just be
patience and spends a few minutes to DIGEST this part. Trust me, it worth the time
and could reward you with plenty of joy with the camera you own.

About
aperture and its direct relation that might affect in your photography:- i.e. Other
than controlling the amount of light entering into the camera, What else does "apertures"
do ?

When
the shutter button is released, light passes through the aperture diaphragm and hit
the film, an exposure is formed. Basically, aperture, along with duration/timing
of the shutter curtain opening, BOTH contribute to a the formation of an exposure.
But aperture also affects an important photographic element called "depth
of field" (short form "DOF"). You may ask, what is hell is this
"Depth of Field" ? Depth of field
is just technical term used to describe the 'zone' of sharpness' between nearest
and furthest of a subject in focus (to be more exact, distance of sharp focus in
front and behind, subject on which the lens is focused).

There
are a few elements that will affects Depth of Field in a picture (Note:- Factors on lens ONLY,
shutter speed never affects depth of field):

1

the lens opening
(diaphragm inside the lens)

the bigger the apertures
used, the zone of sharpness is shallower or vice versa i.e. smaller aperture used
will has extended depth of field

Top
and Bottom:- Typical scenic pictures with a smaller aperture to gain extended depth
of field (sharp zone of focus)

PhilipChong
(44k)

Lovely
blur out (depth of field) on distracting background via use of a combination of telephoto
lens with a large aperture which draws viewer attention to the main subject.

CY Leow (52k)

In
fact, if you still don't understand, just memorize this: Other than it can be used to regulate
amount of light entering into camera for an exposure, aperture also will affect the
degree of depth of field. When
combined with other essential elements that may also contribute to depth of field
changes, such as focal length of the lens in use, the distance of your object in
focus, you can make use of depth of field for creative control in your photography.
For example: use larger aperture (Smaller number like f/2.8, f/2.0 etc.) with
a long focal length to isolate or emphasis on expression, such as in portraiture
photography; or use a smaller aperture (Bigger number like f/16 or f/22
etc..) to ensure pin-sharp details in both the foreground and the background.

Another factor you need to know
is: All the markings on the lens barrel are double in effect . i.e. f/11 doubles
the amount of light of f16, f2 allows 1X more light than of f2.8 does into the camera
etc.

With
a mechanical SLR camera, with the
proper exposure GUIDE suggested by the built-in meter in a camera, you need to adjust
both aperture and shutter speed yourself (it is termed as "MANUAL"
setting in an automatic camera). Usually in the case of an automatic camera,
you will still have manual control operating as if you are using a mechanical camera.
Typically, a few extra choices of exposure control methods may be provided:- the
first is called "Aperture Priority" (some camera uses
a symbol "Av" - short for "aperture value"; the next is
"Shutter
Priority"
(Tv - short for "Timing value". Aperture priority means you
select the aperture to determine the depth of field yourself and the camera will
set to the appropriate shutter speeds to match your aperture selected for a optimum
exposure suggested by the camera's built-in electronic metering circuit, while shutter
priority will let you select the preferred shutter speed setting and the camera
will select the matching aperture values to match your choice. The third option is
called the "Programmed Mode"(P - short for "Programmed
Auto", where the camera select both the aperture value and the shutter speed
for you and you may have no control in determine the depth of field yourself. (some
cameras offer a another mode called flexi-program - I think it is too complicated
to explain here).

Some examples
of how an APERTURE PRIORITY AUTO SLR-type cameras shutter speed ring look like
and comparison made with a fully mechanical SLR type (below - far right)

Nikon FAThis
is a Multi-modes auto SLR. The ring doesn't have an "A", various modes
ae at the side P, S, A and M (Manual)

Nikon FM2nThe
Shutter Speed ring of a MECHANICAL / NON-AUTO SLR. no Auto
selection button or setting. You need to set the shutter speed on the camera section
along with the aperture on the lens. Other brands such as Pentax offers K1000, Olympus
has an OM-1 etc.

Newer range of autofocus
SLR cameras use a new method of controlling aperture. You will find there is NO NEED
to set aperture via the lens aperture ring; instead - aperture is controlled by the
thumb wheel for BOTH shutter Speed (B) and Aperture (A). A method first pioneered by Canon on
their manual focus Camera, the Canon T90 back in 1986. Although this new electronic
input method is different from older SLR cameras, the principle remains the same.
The VISIBLE confirmation of the selected aperture used on camera like this type is
via the LCD on the top panel OR through the viewfinder.

Note:An exposure control ring found in many modern
SLR. The various setting may be represented by a few symbols/letters, "P"
is for "Programmed AE", the "Tv" is for shutter priority
while the Av (aperture value) is referring to aperture priority - Canon's
way of interpreting in their A and T series camera bodies. IF you are a owner of
one of those SLR cameras, you can CLICK HERE to find out the exact model
you are using. While Nikon Owner may use THIS SECTION OR you may find the specific
camera models
that I might have developed with a featured section.

Every camera
manufacturers have different design of how to adjust shutter speeds with a dedicated
AF lens. For an example, Nikon's Nikon F5, 1996/7 finally
followed Canon's path in using wheel input for shutter speed and aperture control;
followed by its next generation AF film/digital-based SLRs which resulted in newer
AF G-series Nikkor lenses now has NO aperture ring on the lens barrel for controlling
aperture. However, if an older manual focus Ai lens is used in manual or aperture
priority AE mode, it will still operate as an conventional SLR in which you will
still make use of the lens aperture scales. Time changes, methods alter but basic
principle remains.

I
strongly advise you to consume
this section first before
you think of proceeding to the next segment on shutter speeds. If you can't
,or finding difficulties digesting what I have prepared here, I'm sorry for my failure
in explaining the essentials. In such cases, I would suggest you to buy a better
illustrated photographic reference book or join a local photographic club. But if
you do understand and have picked up something from this section, you are encouraged
to click at the button underneath and continue...